A magnetic valve or a solenoid injector may be used for injecting fuel into a combustion chamber, for example into a cylinder. A solenoid injector of this type (also referred to as coil-type injector) has a coil which generates a magnetic field when current flows through the coil, whereby a magnetic force is exerted on an armature such that the armature is displaced in order to effect an opening and closing of a nozzle needle or of a closure element for the purposes of opening and closing the magnetic valve. If the magnetic valve or the solenoid injector exhibits a so-called idle stroke between armature and nozzle needle or between armature and closure element, then a displacement of the armature leads to a displacement also of the closure element or of the nozzle needle not immediately but rather only after the armature has been displaced by the extent of the idle stroke.
When a voltage is applied to the coil of the magnetic valve, electromagnetic forces cause the armature to be moved in the direction of a pole piece. By means of a mechanical coupling (for example mechanical contact), after the idle stroke has been overcome, the nozzle needle or the closure element likewise moves (during the working stroke or needle stroke) and, in the case of corresponding displacement, opens up injection holes for the feed of fuel into the combustion chamber. If current continues to flow through the coil, the armature and nozzle needle or closure element move further until the armature arrives at and abuts against the pole piece. The distance between the abutment of the armature against a driver of the closure element or of the nozzle needle and the abutment of the armature against the pole piece is also referred to as needle stroke or working stroke. To close the valve, the excitation voltage applied to the coil is deactivated, and the coil is short-circuited, such that the magnetic force is dissipated. The short-circuiting of the coil results in a polarity reversal of the voltage owing to the dissipation of the magnetic field stored in the coil. The level of the voltage is limited by means of a diode. Owing to a restoring force which is provided for example by a spring, the nozzle needle or closure element including armature are moved into the closed position. Here, the idle stroke and the needle stroke are passed through in the reverse sequence.
The time of the start of the needle movement during the opening of the magnetic valve may be dependent on the magnitude of the idle stroke. The time of the abutment of the needle or of the armature against the pole piece is dependent on the magnitude of the needle stroke or working stroke. The injector-specific time variations of the start of the needle movement (opening) and of the end of the needle movement (closing) may, in the case of identical electrical actuation, result in different injection quantities.
After the armature has overcome the idle stroke for the purposes of opening the magnetic valve (if an idle stroke is present in the magnetic valve under consideration), the armature abuts against the pole piece, which prevents a further movement or displacement of the armature in the direction for opening the magnetic valve. Upon the abutment, the armature may be elastically repelled, and after the armature has been repelled by a certain displacement stroke, it may abut against the pole piece again. In this way, the armature may perform a bouncing movement, in the case of which it is repelled at least once by the pole piece, is accelerated in a direction for the closure of the magnetic valve, and is then in turn accelerated and displaced in a direction for the opening of the magnetic valve owing to the magnetic force that is still acting. The bouncing process may in this case comprise one or more states of abutment of the armature against the pole piece.
The bouncing or the bouncing movement may individually differ for different injectors or magnetic valves, for example with regard to different damping actions owing to mechanical deviations (hydraulic gap), different materials, different elastic characteristics, different masses of the moving parts, in particular of the armature etc. Thus, in different magnetic valves or injectors, different quantity characteristic curves may arise when the injector is closed again during the bouncing process. A closing process may in this case be dependent in particular on whether the armature moves for example in the direction of opening of the valve or in the direction of closing of the valve at the start of an intended closing process.
Furthermore, in the bouncing region, or during the bouncing movement, the injector actuation (in particular the actuation of the magnetic valve for the opening of the magnetic valve) may also be difficult or inaccurate, because a unique dependency of actuation duration (for example duration of the boost voltage and/or duration of a holding voltage interval) and the injection quantity will imperatively not always be present. For example, the injection quantity may decrease despite increasing actuation duration (in particular increasing duration of the boost voltage and/or increasing duration of the holding voltage during a voltage profile).
Thus, in conventional injection systems which use a magnetic valve, inaccuracies may arise with regard to the desired injection quantity of the fuel and also with regard to the desired characteristic of the injection of the fuel with respect to time.
In conventional methods, injection times which exhibit pronounced bouncing behavior in the actuation of the magnetic valve are avoided. It is thus possible for the regions with the adverse effects of the bouncing behavior in the quantity characteristic map to be excluded. The actuation is thus however subject to significant restrictions, which may have adverse effects on the operation of the internal combustion engine.